1. Field of the Invention
The present invention relates generally to perforated materials to be imaged to form one-way vision or other types of vision control panel and their method of imaging.
2. Description of Related Art
Vision control panels are known, for example panels typically comprising a transparent material and a design superimposed on an opaque silhouette pattern, for example a perforated film, as disclosed in U.S. RE37,186 reissued from U.S. Pat. No. 4,673,609, the design being visible from one side of the panel but not from the other side of the panel from which good visibility is obtained through the panel. Other vision control panels have a translucent design visible from one side of the panel superimposed on a translucent “base pattern”, typically a translucent white layer, which enables the design to be illuminated from the other side of the panel, as disclosed in U.S. Pat. No. 6,212,805. Both of these documents disclose perforated self-adhesive assemblies comprising a perforated film layer, a perforated adhesive layer and a perforated release liner. In 1993, Visual Technologies, Inc., NC, USA, conceived the idea of adding an additional non-perforated layer to the perforated liner, initially in the form of a self-adhesive “application tape”, to enable the resultant assembly with a composite liner comprising the perforated release liner and the non-perforated application tape to be imaged by a screen printing press with a vacuum bed. A vacuum bed cannot operate effectively with a substantial proportion of perforations in a substrate. Visual Technologies, Inc. made this idea public in September 1993, all as evidenced in the Reissue of U.S. Pat. No. 5,609,938 and the related Public Use Proceedings in the US Patent and Trademark Office.
The electrostatic transfer imaging of a perforated assembly was also made public in 1993 in the brochure of ImagoImage, Inc., US. The method comprised first printing an image on a transfer medium electrographically with toner. The image was then transferred from the transfer medium to the solid areas only of the perforated vinyl by means of a hot roller laminator. No image material entered the perforation holes. The imaged perforated material typically required a transparent self-adhesive overlaminate to protect the image from UV radiation and abrasion. Also, overlaminates are often applied to perforated materials applied to the outside of a window to avoid rain ingress into the holes. Rain-water forms a meniscus and thereby a lens effect in each hole, which makes the self-adhesive assembly on a window appear like deformé glass, preventing clarity of through vision. Such a self-adhesive overlaminate on an imaged, open, perforated self-adhesive assembly would have resulted in exposed pressure-sensitive adhesive in the holes, causing dust and other impurities that entered the holes to adhere to the pressure-sensitive adhesive before application of the imaged, overlaminated assembly to a window, thereby detracting from through visibility. For these reasons, an additional non-perforated backing layer was also a standard component of self-adhesive assemblies imaged by the electrostatic transfer process, to avoid such contamination. The additional non-perforated layer was incorporated into perforated self-adhesive assemblies for other reasons, for example to prevent paint from the process of air brushing an image passing through the perforated self-adhesive assembly.
U.S. Pat. No. 5,858,155 discloses a perforated adhesive assembly with a non-perforated replacement liner applied to the perforated adhesive layer after removal of a temporary perforated liner, to achieve similar and additional benefits of an additional non-perforated layer.
Even digital imaging systems which would not transmit marking material through the holes used perforated assemblies with a non-perforated layer. For example thermal transfer imaging, for example using a thermal transfer digital press such as the Gerber Edge™ by Gerber Scientific Instruments, Inc., CT, USA, used a perforated material assembly comprising a replacement liner. One reason for this is that perforated materials with a non-perforated layer were the only ones on the market but also the Gerber Edge is sprocket driven, requiring a replacement liner in order to provide a layer of the assembly which can be punched with sprocket holes and which is subsequently strong enough to withstand the sprocket drive mechanism.
Inkjet printing machines for wide-format imaging of large graphics for display and other purposes came into common usage during the mid to late 1990's to become the dominant large format digital imaging system, for example including the printing of bus wraps, building wraps and retail window graphics, using the perforated materials of either the additional liner construction or the replacement liner construction. The solid liner was essential to collect ink which passed through the perforation holes.
In summary, while a simple perforated self-adhesive assembly of perforated film facestock, perforated adhesive layer and perforated liner was disclosed in U.S. Pat. No. 4,673,609, published in 1987, reissued as U.S. RE37,186, such assemblies were impractical and the perforated self-adhesive assemblies for imaging and application to windows available on the market have been one of the above two types with a solid, non-perforated layer, either an additional non-perforated backing layer or a non-perforated replacement liner. Such products have been imaged by a variety of techniques, including screen printing and various digital imaging methods, including electrostatic transfer printing and thermal transfer printing, and UV, solvent, eco-solvent, water-based and latex inkjet printing.
An additional non-perforated backing layer has typically been provided by an opaque white self-adhesive paper “application tape” or by a translucent heat-bonded plastic film; typically a translucent polypropylene or polyethylene film. A replacement liner has typically been of opaque white paper. When imaged with a design and applied to a window, such products are typically intended to be seen from outside the window, for example of a building or vehicle, illuminated by natural daylight or artificial illumination. For one-way vision products, there is typically a black PVC layer or a black adhesive layer facing inwards, such light-absorbing color assisting vision out of the window compared to a more reflective surface. Such products have been manufactured under license to the Contra Vision Ltd (UK) group of companies by licensees including 3M (Minnesota Mining and Manufacturing Company, US), Avery Dennison, Inc., US, FLEXcon, Inc., US, LG Chem (S. Korea) and Orafol (Germany).
If a prior art inkjet printer with a platen had been used for printing perforated materials without an imperforate layer, inkjet ink would have passed through the perforation holes in the perforated material onto the platen and from there be applied to the liner and drawn along in the subsequent movement of the perforated material through the machine. A non-perforated layer in an assembly was conventionally also required for printing on an inkjet printer with a partial vacuum platen or partial vacuum printbed, as the platen or bed comprises holes and a partial vacuum system for holding down the substrate, which could not operate with an open perforated material and which would cause ink to be sucked through the holes. This contamination would eventually seriously damage the machine, as well as the printed product being spoiled by unwanted ink spreading to other parts of the product than where it was intended to be deposited. For these reasons, additional liner or replacement liner perforated assemblies comprising a solid, non-perforated layer have been consistently and invariably used for inkjet imaging of perforated materials.
However, the inkjet printing of the prior art perforated materials with a non-perforated layer has a number of disadvantages depending on the type of inkjet ink being used. With prior art self-adhesive assemblies with an additional non-perforated backing layer, the inevitable distortion of the perforated adhesive assembly during the punching process is “locked in” by the application of the additional non-perforated backing layer. This causes incomplete contact between the pressure-sensitive adhesive and a window following removal of the composite liner of the perforated release liner and the non-perforated backing layer and the application of the self-adhesive film to a window. In contrast, the replacement liner construction allows the pressure-sensitive adhesive to “wet-out” on the plane surface of the replacement liner, providing overall contact between the adhesive and the window with the exception of the hole areas. Replacement liner construction is also preferred for a number of other reasons, including so-called “lay-flat” properties. However, it has been found in practice that when imaging such a replacement liner construction by means of UV curable inkjet ink, in dark areas of the design or other areas of relatively high ink deposition, upon removal of the replacement liner, the UV-cured ink can remain spanning across the holes, either as a continuous layer or a lattice of cured inkjet material. Such blocked holes or partially blocked holes are only identified upon removal of the replacement liner, typically on site during application to a window, when removal of the ink blockages is extremely difficult, if not totally impractical.
Separately, when imaging the replacement liner construction with solvent inkjet ink, the ink entering the holes lies and coalesces on the release surface of the replacement liner and is relatively difficult to dry, as it is removed from and relatively protected from the passage of any drying air across the surface of the material. It has been found that, if such coalesced droplets migrate to the edges of the holes, solvents in the ink can deleteriously affect the subsequent performance of the pressure-sensitive adhesive contiguous with the release surface of the replacement liner. The difficulty of drying inkjet ink residing in perforation holes also applies to water-based inkjet inks and the so-called “latex” inkjet inks sold by Hewlett Packard, CA, USA. Such uncured inkjet ink residing on the surface of the liner can also cause discoloration of the adhesive which is particularly damaging with clear perforated materials for inside application to a window, as the discolored adhesive will be visible from outside the window. U.S. Pat. No. 7,897,230 discloses an “ink retention layer” to absorb excess solvent based ink that can otherwise migrate to and detract from the performance of the adhesive layer.
Solvent ink which coalesces into globules on the exposed release surface of the liner, only covers a small percentage of the exposed hole area, the remainder typically remaining white and thus lightening the perceived image, providing a pale, “washed-out” impression. This effect causes additional amounts of ink to be applied to perforated materials in an attempt to overcome this problem. It has been found that printing companies and even inkjet machine manufacturers consistently input machine settings to apply more ink than is necessary and thus require more curing than is necessary, when imaging these prior art perforated materials with a white or translucent non-perforated layer, wasting curing energy as well as ink. WO 2008/149301 discloses a gray, non-perforated additional layer or replacement liner visible through the perforation holes to overcome these problems.
Digital inkjet imaging systems with an “open gutter” or “ink collector” instead of a conventional solid or partial vacuum platen are known in the field of imaging open fabrics (woven or non-woven) or mesh materials without a non-perforated backing layer. Excess ink which passes through the open areas or voids in the fabric or mesh material is collected in a gutter, typically containing an absorbent removable material such as blotting paper or plastic foam material. However, digital inkjet machines with an open gutter to print fabrics typically comprise a relatively complex handling system to cater for and counteract the dimensional instability of fabric that would otherwise cause unacceptable loss of printing registration and other potential defects in the finished printed product. Thus such machines developed for the printing of fabrics by digital inkjet have an arrangement of tension and other control devices in order to transport the fabric through the printing press in a manner that is intended to minimize geometric distortion of the fabric, which would otherwise worsen the lack of registration between successive printhead passes over the fabric or caused by movement of the fabric and can even lead to unprinted areas in folds of fabric. Fabrics and meshes are typically of light weight in relation to their in-plane tensile strength, especially in the direction of the weft. It is important that the fabric is tensioned across an open gutter, to minimise variation in the distance between the inkjet printheads and the fabric being printed, the so-called “print distance”, as this dimension affects the quality of the resultant print. The tensioning devices on such machines for use with an “open gutter” are designed for fabrics, which typically have a very low mass/tensile strength ratio. Fabric printing machines typically have a relatively long lead length passing through an array of rollers controlling the tension in the fabric.
Conversely, inkjet printing machines for printing self-adhesive vinyl assemblies typically have ‘push’ feed nip rollers, not the tensioned pulling nip rollers used for fabric printing. The self-adhesive vinyl has sufficient flexural rigidity to be pushed forward and be temporarily held down by a suction platen while being printed and then released and fed forwards. This preferable arrangement enables the self-adhesive vinyl assembles to be cut immediately after the zone of printing, whereas fabric inkjet printers require continuous roller feed and take-up configurations to maintain the required tension feed, causing leading and trailing wastage of material. This separation of technology and use for fabric and mesh printing as opposed to self-adhesive vinyl and other substrates was of common general knowledge as well as known to one of ordinary skills in the art, summarised in “Industrial Inkjet for DUMMIES” published by Wiley Publishing, Inc. in 2010, page 41 “Textile printing machines look very much like a typical digital wide-format printer with special materials-handling systems to ensure that the textile is firmly held in place.”
EP 2103443 A1 discloses a perforated one-way vision film comprising a base material with an adhered foam layer that will adhere to a window before and after inkjet imaging with a design, the base material being a film or non-woven fabric, and the imaging of fabric products by an inkjet printer with an ink collector.
U.S. Pat. No. 5,550,346 and U.S. Pat. No. 5,679,435 disclose the laser perforation of retro-reflective self-adhesive assemblies. Perforation by laser typically results in a dark, burnt perimeter to each of the perforation holes.
Prior art one-way vision perforated materials comprising a white layer suffer from a “ghost image” being visible from the side of the panel remote from the design, owing to inkjet ink which is deposited on the inside edges of the holes being visible against the white layer, especially when viewed from an acute angle to the one-way vision panel. Incomplete deposition of ink upon in-hole white material also results in amended perceived colors when seen at acute angles from the imaged side of the panel, for example the “whitening” or reduction in graytone of dark colors. Further, through-vision at acute angles is impaired by white material being visible from the through-vision side of the panel, black being the ideal color to allow through vision through the adjacent holes.